Thermoplastic molding compositions based on aromatic polycarbonates and those based on aromatic polyester carbonates are well known. The physical and mechanical properties of these compositions make them suitable as engineering resins for a large variety of applications where durability and optical clarity are required. Due however to their relatively high melt flow indices, these materials are not easily processible and improvements have been sought. Notable in this regard is U.S. Pat. No. 4,778,855 which describes compositions containing a copolyetherester which consists essentially of a multiplicity of recurring intralinear long chain and short chain ester units connected head to tail through ester linkages.